Three-conductor cable



Dec. 17, 1929. w. c. HAYMAN THREE-CONDUCTOR CABLE Filed Aug. 25. 1928FLQI.

Inventor WLLLLam C. fiagmcm, 3 M 71,@m/ HLE Attorney.

Patented Dec. 17, 1929 UNITED STATES PATENT OFFICE WILLIAM C. HAYMAN, OFSCHENEGTADY, NEW YORK, ASSIGNOR-TO GENERAL IQLECTRIC COMPANY, A.CORPORATION OF NEW YORK THREE-CONDUCTOR CABLE The present inventionrelates to the type of electric cable comprising multiple conductors,each of which is suitably insulated, an enclosing sheath and a passageor channel inside the sheath for fluid insulation, such as oil, whichfluid impregnates the insulation.

The object of my invention is to provide a cable of the above mentionedtype which is of improved construction, particularly with respect to themeans which form the fluid passages or channels.

For a consideration of what I believe to be new and my invention,attention is directed to the accompanying description and the claimsappended thereto. I

In the drawing which is illustrative of my invention, Fig. 1 is across-section of a cable; Fig. 2 is a short length of" cable, and Fig. 3is a detail view of one of the oil channels.

4 indicates the conductors of which three are shown-spaced 120 apartabout a common center. They are shown as being of the sector type orshape which has the advantage among other things of permitting asomewhat greater amount of metal, such as copper, for a given diameterof sheath than where they are circular in cross-section. Also thearrangement decreases the liability of crushing of the cable sheath inreeling and installing. I may, however, utilize conductors which aredifferently shaped in cross-section. Each conductor is tigditly wrappedwith paper or equivalent insulation 5. Outside of the insulation is atightly wrapped or metal or metalized body 6 which in the presentinstance comprises a thin metal ribbon which has numerous and usuallyequally spaced holes or perforations 7 and through which oil is free topass and permeate the insulation. The ribbon on each conductor is inelectrical and mechanical contact with those on the other conductors andis also in electrical communication with the outer casing or sheath 8.These ribbons serve to distribute thmec'fi'ical stresses and also serveto convey heat from the inside of the cable to the sheath. It isdesirable to space the turns one from the other by a slight amount so asnot to impede the free passage of oil to and from the paper. It is alsodesirable to so arrange the perforations that the resistance to flow ofcurrent is the same in all directions. This is done by making theperfora-. tions of the same size and spacing them equally. Theconductors are laid up in such a way as to form long pitch spirals as iscustomary in cable construction. The conductors are tightly boundtogether by a thin strip of metal 9 which to distinguish it from theperfo rated ribbon or metalized bodies will be called a tape. The tapein addition to preventing the conductors from spreading due to anycause, such for example as heavy load conditions or bending of the.cable in reeling and in installing, establishes electrical connectionsbetween the perforated ribbons and the sheath 8.

In the construction thus fardescribed there are three spaces or channels10 which are located one hundred and twenty degrees apart and also onein the center where the ribbons do not make contact, for the receptionof oil. In each of the outer spaces is located a I metal tube 11 whichforms an oil channel or passage, said tubes being spirally arranged,following in this particular the lay of the cable conductors. Thesetubes also serve the important function of preventing the collapse ofthe lead sheath 8 due to any cause. In addition these tubes must be soconstructed as to permit oil to freely pass from them into the spaces inwhich they are located. Moreover, they must be flexible in order not tointerfere with the bending of the cable, or on the other hand be crushedor deformed by such bending. Lastly and which is the most importantfeature of all from a manufacturing point of view they must be of such acharacter as not to change in diameter due to elongation or otherwise asthey are fed into place from bobbins or other supports in the cablingmachines, meaning thereby the machines in which the several conductorsand their coverings are stranded or formedinto a cable.

A form of tubing which has all of these necessary and desirablequalities is illustrated in Fig. 3. This tubing is formed from arelatively thin strip of metal 12, say of the order of 10 to 15 mils inthickness, which is wound in spiral form With interlocked edges bysuitable dies. As finally shaped each turn has a portion 13 of largediameter and another portion 14 of smaller diameter the latterinterlocking with the portion of larger diameter of the adjacent turn.The larger portion of each turn has an internal shoulder 15 whichinterlocks with an external shoulder 16 on the portion of smallerdiameter of the adjacent turn. These interlocking shoulders prevent thetube from elongating in the cabling operation and hence preventreduction in diameter due to that cause. The portions 13 are of archedconstruction and due to this and to the interlocking shoulders offergreat resistance to crushing or deforming strains which strains if greatenough to crush the tube would decrease the diameter of its bore,interfere with the flow of oil and deform the cable as a whole. For themetal strip I may in some cases use a non-magnetic metal, such ascopper, zinc or aluminum, while in other cases I may use a magneticmetal such as iron or steel. \Vhen magnetic material is used theinsulations on the conductors should be covered with shielding meanssuch as the perforated ribbon or equivalent metalized surface.

Such a tube can be bent at a considerably smaller angle than the cableitself, is very strong, and while the turns engage one another and arereasonably tight fitting oil will readily pass through the joints intothe surrounding spaces from which it is free to enter the insulation onthe conductors and also the central space between the condu torcoverings.

In addition to the features above enumerated the tubes are goodconductors of heat picking it up from the perforated ribbons around theconductors and from the oil and conveying it to the surrounding steeltape from which the heat passes directly to and through the sheath. Thefact that after the steel tape is tightly wound over the conductors andtubes the structure thus formed is not truly cylindrical but is slightlyflattened in the space between each tube and the adjoined conductorcoverings has the advantage that the tape contacts with the tube over aconsiderable area and in this manner improves the heat conductivity ofthe parts.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In an electric cable, the combination of a number of insulatedconductors arranged about a common center, an enclosing sheath, therebeing spaces between each pair of conductors and the inner wall of thesheath, and flexible metal tubes, each comprising a spirally wound stripof metal having overlapping edges to prevent crushing, located in saidspaces which supply fluid insulation to the thereto, metallic tape whichbinds the conductors and tubes, and a sheath which surrounds the tapeand forms a fluid tight closure for the cable.

3. In an electric cable, the combination of a plurality of insulatedconductors arranged about a common center, an enclosing sheath, therebeing a peripheral space between each pair of conductors and the innerwall of the sheath, a flexible metal tube located in each of said spacesand comprising a spirally wound strip of metal, the edges of each turninterlocking with the edges of adjacent turns to prevent deformation,said tubes supplying fluid insulation to the spaces and insulation andalso assisting to support the sheath.

4. In an electric cable, the combination of a plurality of sector shapedconductors, a body of insulation for each conductor, a metallic coveringfor each of said bodies, a flexible metal tube comprising a spirallywound strip of metal having overlapping and interlocking edges which isin mechanical and electrical contact with the metallic covering ofadjacent conductors, supplies fluid to the insulating bodies, assists insupporting the sheath in the region between two conductor coverings andtransmits heat from the conductors and fluid to the sheath.

5. In an electric cable, the combination of a plurality of insulatedconductors arranged about a common center, tubes located in the spacesbetween the conductor coverings to supply fluid to the insulation eachof which is made of a spirally wrapped strip of metal, each of the turnsof said strip having an arched portion and edges which interlock withthe edges of adjacent turns to prevent deformation, a metal tape whichbinds the parts together and rests on the insulated conductors and alsoon the metal tubes, and an enclosing sheath.

In witness whereof, I have hereunto set my hand this 23rd day of August,1928.

WILLIAM C. HAYMAN.

